Before you think about panel brands or prices, look up. Your roof decides a lot about how well solar will work for you. The direction it faces, the shade it gets, its age and what it is made of all change how much power you make and what you pay.
The good news is that most roofs work fine. Perfect is not required. This guide shows you what to check, with rough numbers, so you know what to expect before an installer visits.
Which direction should your roof face?
In the US and other northern places, a south-facing roof gets the most sun over a year. East and west roofs still do well. North-facing roofs are the weakest.
| Roof direction | Rough yearly output vs. south | Notes |
|---|---|---|
| South | 100% | Best overall |
| Southeast / southwest | 95% to 97% | Nearly as good |
| East | 80% to 85% | More morning power |
| West | 80% to 85% | More late-day power, which can help on time-of-use rates |
| North | 55% to 70% on low slopes, much less on steep ones | Usually a poor fit |
Here is a worked example. A 6 kW system on a south roof in a sunny state makes about 9,000 kWh a year. On a west roof, at about 82%, it would make roughly 9,000 × 0.82 = 7,380 kWh. That is less, but still a lot of power.
Many homes put panels on two sides, such as east and west. That spreads production across the day. A west roof also lines up well with evening peak prices if your utility uses time-of-use rates.
Does roof tilt matter?
Yes, but less than most people think. In most of the US, tilts between about 15 and 40 degrees all work well. The ideal angle is close to your latitude, but being off by 10 or 15 degrees often costs only a few percent.
A common roof pitch, called 6/12, is about 27 degrees. That is near ideal for much of the country. Very flat roofs lose a little and collect more dirt. Very steep roofs can shed snow well but may lose some summer output.
On flat roofs, installers use tilted racks to angle the panels up. This helps output and lets rain wash them.
How much does shade hurt solar output?
Shade is often a bigger problem than direction. A tree or chimney that shades part of your roof during the middle of the day can cut output a lot.
The most important sun hours are roughly 9 a.m. to 3 p.m. Shade in the early morning or late evening matters much less. Winter shade is tricky, because the low sun casts long shadows. A tree that looks harmless in June might shade your roof all of December.
How panel electronics help
On older systems, shade on one panel could drag down a whole row. Today, many systems use microinverters or power optimizers. These let each panel work on its own, so one shaded panel does not pull down the others. Learn these terms in our solar glossary.
A quick check: stand outside a few times on a sunny day and note where shadows fall on your roof. Installers use satellite tools and shade meters to measure this more exactly. If you have tall trees, trimming a few branches may be cheaper than losing 10% to 20% of your output for 25 years.
How old is too old for your roof?
Solar panels often last 25 to 30 years. If your roof will need replacing in a few years, you will have to pay to remove and reinstall the panels. That job often costs a few thousand dollars, sometimes $3,000 to $6,000 or more for a typical home.
A rough guide to roof life:
- Asphalt shingles: about 20 to 30 years
- Metal: about 40 to 70 years
- Clay or concrete tile: 50 years or more, though the underlayment may need work sooner
- Flat membrane (TPO, EPDM): about 15 to 30 years
Worked example: your asphalt roof is 18 years old and rated for 25. That leaves about 7 years. Adding panels now means paying to remove them in 7 years. Replacing the roof first is likely the better plan.
Does your roof material change the install?
Most common materials work. Some cost more or take more care.
| Material | Solar fit | What to know |
|---|---|---|
| Asphalt shingle | Very good | Most common and usually lowest install cost |
| Standing-seam metal | Excellent | Clamps attach to seams with no holes; long roof life |
| Corrugated metal | Good | Needs sealed mounts through the panels |
| Clay or concrete tile | Fair | Tiles can crack; special hooks add labor cost |
| Slate or wood shake | Hard | Fragile or fire concerns; fewer installers will do it |
| Flat membrane | Good | Uses weighted or attached tilt racks; check drainage |
Ask any installer how they seal roof penetrations and what warranty covers leaks. A good installer will offer a workmanship warranty that covers the roof where they attached mounts.
Will your roof hold the weight?
Solar panels and racking add about 2 to 4 pounds per square foot. Most roofs built to modern codes can carry that easily. Older homes, roofs with sagging, or roofs that already have two layers of shingles may need a closer look.
Your installer should check the roof's structure as part of the design. In many areas, the permit also needs a review of the framing. Signs of trouble include sagging lines, soft spots, water stains in the attic or rot near the eaves. Fixing these first is a must.
All electrical work that connects the system to your home panel should be done by a licensed electrician. Your installer will usually handle this and the permits.
When does a ground mount make more sense?
If your roof faces north, is heavily shaded, is too small or is in poor shape, a ground mount can be a great option. You set the panels in an open part of your yard, facing south at the best angle.
- Pros: best direction and tilt, easy to clean and inspect, no roof holes, easy to expand later
- Cons: often costs 10% to 25% more per watt, needs open yard space, needs trenching for the wiring
Because a ground mount faces the ideal way, it can make more power per panel. A system that would make 80% on an east roof might make 100% on the ground. That gain can cover some of the extra cost.
What should you do next?
Start by checking direction, shade and age yourself. Then get a rough sense of how big a system you need with our system size tool, and estimate savings with the savings calculator. When you are ready, compare installer quotes through our quotes page. If winter weather is a worry, see how solar handles snow and clouds.
Frequently asked questions
Can I put solar on a north-facing roof?
You can, but output is often much lower, especially on steep roofs. Most installers will suggest other roof faces or a ground mount instead.
Will solar panels damage my roof?
A good install should not. Mounts are sealed with flashing, and panels can even shield the roof from sun and hail. Ask about the installer's leak warranty.
How much roof space do I need?
A typical panel is about 18 square feet. A 6 kW system with 15 panels of 400 watts needs about 270 square feet, plus space for setbacks required by fire codes.
Should I replace my roof before installing solar?
If your roof has less than about 10 years of life left, yes. Replacing it first avoids paying to remove and reinstall panels later.
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